How to Fix ValueError: The truth value of an array with more than one element is ambiguous

Python raises ValueError: The truth value of an array with more than one element is ambiguous when trying to operate on an array with multiple elements, but the operation expects a single boolean value.

The reason for this error is that NumPy does not allow direct evaluation of the truthiness of an entire array because it is ambiguous whether the truthiness should be determined element-wise or if it should evaluate the whole array as a single object.

To fix ValueError: The truth value of an array with more than one element is ambiguous error, you can use the “np.any()” or “np.all()” function to check whether the array is empty. These functions return True if any or all of the elements of the array are True, respectively.

Method 1: Using the np.any() function

To check if an array is empty, you can use the “np.any()” function.

import numpy as np

arr = np.array([1, 2, 3, 4])

if np.any(arr):
  print("The array is not empty")

Output

python3 app.py

Method 2: Using the np.all() function

Use the “np.all()” function to check if all elements in the array meet the condition.

import numpy as np

arr = np.array([1, 2, 3, 4])

if np.all(arr > 0):
  print("All elements are greater than 0")

Output

All elements are greater than 0

Method 3: Using the np.size function

Use the size attribute or “np.size()” function to check if the array is empty.

import numpy as np

arr = np.array([1, 2, 3, 4])

if np.size(arr) == 0:
  print("Array is empty")
else:
  print("The array is not empty") 

Output

The array is not empty

Remember to use the appropriate condition-checking function based on your specific use case.

That’s it.